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Aug. 1, 2012 -- Older women with the most common type of metastatic breast cancer may soon have a new treatment option that may improve their survival.

A new study shows that postmenopausal women with advanced disease treated with a combination of two anti-estrogen therapies lived longer than women who took one drug followed by another.

The study is the first to show that combination hormonal therapy can slow disease progression and improve survival in advanced breast cancer, says researcher Kathy Albain, MD, of Loyola University Medical Center.

The research appears in the Aug. 2 issue of the New England Journal of Medicine.

"This is exciting because we have not seen progression-free survival of this length or any length in these women with previous treatments," she tells WebMD.

Two Anti-Estrogen Drugs Better Than One

The study included close to 700 postmenopausal women with previously untreated, advanced, hormone-receptor-positive breast cancer.

Both drugs are widely used to treat breast cancer, although not at the same time.

Taken by pill, Arimidex works by decreasing the amount of estrogen the body produces.

Given by injection, Faslodex helps to get rid of estrogen receptors and blocks the hormone's effect on cancer cells.

About half the women in the study received standard treatment with Arimidex followed by Faslodex if their disease progressed. The rest took the two drugs together from the time they enrolled in the trial.

Compared to women in the standard treatment group, women who took the combination therapy survived about six months longer -- meaning that for some women the benefit was even greater.

The combination therapy also appeared to slow the progression of their disease and it was well tolerated with a side effect profile similar to that of single-drug treatment.

Three years into the trial, women taking the combination therapy were 13% more likely to have stable disease with no evidence of progression, Albain says.

Combo Treatment May Work for Early Disease

The researchers believe the two drugs' different modes of action may explain why they seem to work better in combination than on their own.

"The majority of deaths from breast cancer occur in women who are hormone-receptor positive because the majority of breast cancers are hormone-receptor positive," researcher Rita S. Mehta, MD, tells WebMD. "We had almost given up on the idea that we would ever see an overall survival benefit in these women."

Mehta is an associate professor of medicine with the Chao Family Comprehensive Cancer Center and an oncologist with the University of California Irvine Breast Health Center.

The next step is to determine if the combination approach can improve cure rates in patients with early-stage disease that has not spread beyond the breast, Mehta and Albain say.

"Whenever we find something that works in advanced disease we want to find out if it can also be useful earlier," Albain says.

The study was funded by the National Cancer Institute and drugmaker AstraZeneca, which markets Arimidex.